Hardness and phase analysis of IN 718 deformed at high strain rate.

Specimens of the nickel base alloy IN 718 deformed at high strain rate (approximately 10 s(-1)), as realized in a screw press, have higher strength than parts forged conventionally in a hydraulic press. Microstructure analyses in light and transmission electron microscopes reveal the precipitation of very small Ni(3)Nb particles (gamma"-phase) to be the reason for the increased hardness. Several processing routes are discussed and analyzed in relation to the TTT-diagram of IN 718.

High-Temperature In Situ Straining Experiments in the High-Voltage Electron Microscope.

: Design rules are described here for high-temperature straining stages for transmission electron microscopy. Temperatures above 1000 degreesC can be attained by electron bombardment of the specimen grips. Thermal equilibrium can be reached in a short time by carrying off the heat by water cooling. Some applications of this stage are described. Ferroelastic deformation was observed at 1150 degreesC in t' and partially stabilized zirconia, which changes the microstructure for successive dislocation plasticity. In the oxide-dispersion-strengthened alloy INCOLOY MA 956, dislocations are impeded by oxide particles and move smoothly between the particles. At high temperatures, both the resting and traveling times control the average dislocation velocity. In MoSi2 single crystals of a soft orientation, dislocations with 1/2<111> Burgers vectors are created in localized sources and move on {110} planes in a viscous manner. The dislocations in Al-Pd-Mn single quasicrystals are oriented in preferred crystallographic directions and move in a viscous way as well. On the basis of in situ observations, conclusions are drawn for interpreting macroscopic deformation behavior at high temperatures.